This invention relates to the field of screws having holding or retaining means incorporated therein.
One of the major problems with conventional screws is that they tend to become loose and in some cases fall completely out of the work piece in which they had been seated.
The inventor of the invention described herein has had a search made to determine the state of the prior art. The only patents found by those who conducted the search are design U.S. Pat Des. Nos. 103,304 and 223,560 neither of which show any holding or retaining means incorporated therein to resist loosening or unintentional removal of the screw, and utility U.S. Pat. Nos. 937,577; 2,195,685; 2,936,667; 3,386,138; 3,461,769; and 4,253,509. No. 937,577 is actually an extension bolt and it includes holding means only in the sense that a threaded cap or nut member is received on the threaded shank of the bolt. U.S. Pat. No. 2,195,685 discloses a telescoping stud which compresses against a coil spring and to that extent the coil spring provides some resistance to loosening. U.S. Pat. No. 2,936,667 discloses a T-slot bolt having a pair of set screws reachable from the inner facing surface of the bolt head to tighten against a surface of the T-slot to keep the bolt from sliding back and forth in the slot. U.S. Pat. No. 3,386,138 discloses a release type of bolt which separates from its retaining nut under pressure. The only holding means is actually the nut. U.S. Pat. No. 3,461,769 discloses an adjustable length screw, in which the only retaining or holding means is the threaded tap 18a itself and to some extent the separate biasing spring 19. U.S. Pat. No. 4,253,509 discloses a theft deterrent locking nut, in which the threaded shanks and threaded bores constitute the holding or retention means. None of the patents found by those who did the search for this inventor disclose any built-in holding or retention means incorporated into the screw body itself to resist loosening or unintentional removal of a threaded screw in an application where a separate threaded nut or threaded tap of some kind cannot be used, nor a separate compression spring to provide a constant bias against the inner face of the screw head.
The invention disclosed herein solves the problem of screws loosening and falling out unintentionally by providing a built-in retention member comprising a stem seated in a central cavity of the screw body having diagonally extending projections which can extend through the side wall of the screw body to bite into the material of the work piece in which the screw is seated and which can be withdrawn into the interior of the screw body when it is desired to remove the screw, by moving the stem of the retention member axially inwardly and outwardly of the screw body.